**Core Concept**
The "Adder Head" appearance is a classic radiological sign observed in intravenous urography (IVP), representing the characteristic shape of the renal pelvis and calyces when visualized on a contrast-enhanced X-ray. It reflects the normal anatomy of the collecting system, where the renal pelvis projects like a snake's head, with the calyces extending like the body of the snake.

**Why the Correct Answer is Right**
In IVP, intravenous contrast is injected and excreted by the kidneys, allowing visualization of the urinary tract. The renal pelvis and calyces form a "bottle brush" or "adder head" appearance due to the tapering, elongated shape of the collecting system. This sign is especially prominent in lateral and anteroposterior views and is a hallmark of normal urinary tract anatomy on IVP.

**Why Each Wrong Option is Incorrect**
Option A: X-ray – While IVP is a type of X-ray, the "adder head" appearance is specific to contrast-enhanced IVP, not plain X-ray. Plain X-rays lack contrast and do not show this feature.
Option B: USG – Ultrasound does not use intravenous contrast and does not visualize the renal pelvis in the same way. The "adder head" sign is not seen on USG.
Option D: CT – CT provides cross-sectional images and does not typically show the "adder head" appearance; it is not a defining feature of CT urography.

**Clinical Pearl / High-Yield Fact**
The "adder head" sign is a key diagnostic feature in IVP to assess renal anatomy and detect obstruction or dilatation. Its absence may suggest obstruction or congenital anomalies, and its presence indicates normal urinary flow.

✓ Correct Answer: C. IVP